Hydrogen-powered fuel cell vehicles typically employ high-pressure tanks or other vessels containing compressed hydrogen gas. Such high-pressure vessels often include one or more pressure relief devices. Such pressure relief devices may be located at an end of the high-pressure vessel at which location various valves, pressure regulators, connectors, excess flow limiters, and the like may be located to allow the vessel to be filled with compressed hydrogen gas to “re-fuel.”
Such pressure relief devices may be thermally activated. In other words, when the hydrogen gas is exposed to high temperatures, the pressure relief device may be activated to relieve pressure that otherwise could result in rupturing of the vessel. Some such pressure relief devices comprise a fragile bulb comprising a liquid that is exposed to heat from the vehicle and/or vessel. When heated to a predetermined temperature, the bulb is configured to burst, thereby opening a vent and allowing the hydrogen gas to exit the vessel.
However, since such devices may rely on the presence of a liquid in order to burst at the predetermined temperature, it may be imperative that a user or technician be notified in the event that the bulb loses some or all of its liquid. This may occur, for example, if the bulb cracks but does not fully burst.
The present inventors have therefore determined that it would be desirable to provide apparatus, methods, and systems for inspecting and/or sensing defects in a thermal pressure relief device in order to detect, for example, losses in fluid in the bulb of such a device and/or defects in a condition of the bulb, and/or in order to overcome one or more other limitations of the prior art.